A Travelling Crane is an overhead lifting machine where a hoist rides a trolley along a bridge girder, and the bridge itself rolls along a pair of elevated runway rails spanning a building bay. Unlike a fixed jib or gantry that covers only an arc or a single line, a travelling crane services the entire rectangular floor area beneath it. The point is to lift heavy loads off the floor and place them anywhere in the bay without forklifts, slings on cranes, or crawler equipment. A typical shop bridge crane handles 5 to 50 tonnes over a 15 to 30 m span at lift speeds of 3 to 8 m/min.
Travelling Crane Interactive Calculator
Vary crane span, rail error, and deflection criterion to see runway alignment limits, girder deflection allowance, and end-truck geometry.
Equation Used
This calculator follows the travelling crane geometry checks stated in the article: runway rails should be parallel within span/1000, bridge girder deflection is limited by L/R, and end-truck wheel base should be at least span/7 to reduce skew.
- Span is the rail-to-rail bridge span.
- Runway rail parallelism limit uses span/1000.
- Girder deflection limit uses the selected L/R criterion; CMAA example uses L/800.
- Minimum end-truck wheel base uses span/7.
Inside the Travelling Crane
A travelling crane works on three independent motions stacked together — long travel along the runway, cross travel of the trolley along the bridge, and hoisting of the load itself. The bridge is a welded box girder or rolled I-beam spanning the bay, supported at each end by an end truck. Each end truck carries two flanged wheels riding on a runway rail bolted to the top of a runway beam, which in turn sits on brackets off the building columns. A long travel motor on each end truck drives the wheels through a gearbox, and the trolley with its hoist drum drives across the bridge on a separate cross travel motor. Three motions, three independent controls, and the hook can reach any point in the bay.
The geometry has to be right or the crane fights itself. The two runway rails must be parallel within roughly span/1000 — on a 20 m span that is 20 mm — otherwise the end trucks skew, the wheel flanges grind against the rail, and you get the classic crab-walking symptom where the bridge crawls diagonally and one motor draws double current. Rail elevation between the two sides must match within about 10 mm or the bridge runs downhill on its own. The bridge girder itself is sized for L/600 to L/800 deflection under rated load — stiffer than a typical floor — because a sloppy girder lets the trolley roll toward midspan under gravity and makes precise spotting impossible.
Failure modes are predictable. Wheel flange wear is the most common, caused by skew from out-of-square end trucks or a worn runway. Hoist brake fade shows up as load drift after the operator releases the up button — usually a glazed brake disc or low coil voltage on the DC brake. And on older Demag or Konecranes units, the festoon cable trolleys jam if the runway is dusty, dropping power to the trolley mid-bay.
Key Components
- Bridge Girder: The main horizontal beam spanning the bay, usually a welded box section for spans over 15 m or a rolled W-shape for shorter spans. Designed to L/800 deflection at rated load per CMAA Specification 70 — a 20 m span deflects no more than 25 mm with the trolley centred and full hook load.
- End Truck: The wheeled carriage at each end of the bridge that rides the runway rail. Carries two or four flanged wheels, the long travel gearmotor, and the rail sweeps. Wheel base must be at least 1/7 of the span or the bridge skews under acceleration.
- Runway Rail and Beam: ASCE 60 or 85 lb/yd crane rail bolted with rail clips to a runway beam supported off the building columns. Rail-to-rail parallelism within span/1000 and elevation match within 10 mm — outside that the wheel flanges wear and the bridge crab-walks.
- Trolley and Hoist: The trolley rolls across the top or bottom flange of the bridge girder and carries the wire rope hoist drum, motor, gearbox, and brake. Hoist drum is grooved for a single layer of rope on hooks rated CMAA Class C or higher to prevent rope crossover and crushing.
- Long Travel Drive: One gearmotor per end truck driving one or both wheels on that side. Two-motor arrangement requires VFDs synchronised within 2% slip or the bridge skews. Typical travel speed is 20 to 40 m/min on a Class C shop crane.
- Festoon or Conductor Bar Power: Flat festoon cable on a C-track delivers three-phase power and control to the moving trolley and bridge. Conductor bars (insulated copper rails with sliding shoes) replace festoon on long runways above 60 m. Festoon trolleys must roll free or the cable rips at the strain relief.
- Pendant or Radio Control: Operator interface giving up/down, north/south, east/west commands plus an emergency stop. Two-step contactor pendants give creep/full speed; VFD radio remotes give infinitely variable speed and are standard on lifts above 10 tonnes.
Real-World Applications of the Travelling Crane
Travelling cranes show up anywhere a heavy item needs to be lifted off the floor and placed somewhere else in the same building. The decision to use one over a forklift or gantry comes down to load weight, lift height, and how often the move happens — once you cross 5 tonnes or need to land a load on a machine bed at height, the overhead bridge crane wins on safety and cycle time. Spans run from 8 m in a small fab shop to over 40 m in a steel mill bay, and capacities span 250 kg pneumatic chain hoists up to 500 tonne ladle cranes in a foundry.
- Steel Mill: ArcelorMittal Dofasco hot strip mill in Hamilton runs Konecranes ladle cranes at 350 tonne capacity over 30 m bays to transfer molten steel from the BOF to the continuous caster.
- Wind Turbine Assembly: Vestas blade plants use 80 tonne double-girder bridge cranes from Demag spanning 36 m to lift completed 70 m blades onto transport cradles.
- Machine Shop: A typical CNC job shop fits a 5 tonne single-girder underhung crane from R&M or Harrington over a 12 m bay to load fixtures onto a Mazak HCN-6800 horizontal machining centre.
- Power Generation: Powerhouse cranes at hydroelectric stations like BC Hydro's Revelstoke unit use 250 tonne EOT cranes to pull the generator rotor for inspection on a 10-year cycle.
- Foundry: Iron foundries use 20 to 50 tonne pendant-controlled bridge cranes with insulated hooks to move ladles of grey iron from the cupola to the pouring line, typically a Street Crane or Stahl unit.
- Aerospace: Boeing's Everett 777X final assembly bay runs a fleet of overhead cranes spanning 90+ m to position wing skins and fuselage sections onto the major join tooling.
- Paper Mill: A 30 tonne winder crane at the dry end of a Voith paper machine lifts finished 25 tonne mother rolls off the reel and onto the slitter.
The Formula Behind the Travelling Crane
The number you size a travelling crane around is wheel load — the vertical force one bridge wheel puts on the runway rail when the trolley sits at the worst-case position with full hook load. Get this wrong and either the runway beam yields or the wheel rim splits. At the low end of the typical operating range — trolley parked at the far end of the bridge — one end truck carries almost the entire load and its wheels see peak force. At the high end of efficiency — trolley centred — both end trucks share the load roughly equally and wheel loads are minimum. The sweet spot for sizing is always the worst case: trolley at the end stops, with rated hook load, plus an impact factor for hoisting acceleration.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Pwheel | Maximum static + impact wheel load on the rail at one end truck | kN | lbf |
| Wbridge | Self-weight of the bridge girder and walkway | kN | lbf |
| Wtrolley | Trolley and hoist dead weight | kN | lbf |
| Wload | Rated hook load (lifted load) | kN | lbf |
| L | Bridge span (rail centre to rail centre) | m | ft |
| a | Trolley distance from the near rail (worst case = trolley end-stop offset) | m | ft |
| φ | Hoist impact factor per CMAA 70 (typically 0.15 to 0.25) | dimensionless | dimensionless |
| nwheels | Number of wheels per end truck (usually 2 or 4) | dimensionless | dimensionless |
Worked Example: Travelling Crane in a shipyard panel shop in Ulsan
A shipyard panel line in Ulsan, South Korea is specifying a single-girder EOT travelling crane to move 10 tonne stiffened steel panels from the one-side welder onto a transfer car. The bay span is 22 m, the chosen Hyundai-built bridge girder weighs 6.5 tonnes, the trolley with hoist weighs 1.8 tonnes, and the trolley end-stop sits 0.6 m from the rail centreline. The shop runs CMAA Class D duty so the impact factor is 0.20. Each end truck has 2 wheels.
Given
- Wload = 98 kN (10 t)
- Wtrolley = 17.7 kN (1.8 t)
- Wbridge = 63.8 kN (6.5 t)
- L = 22 m
- a = 0.6 m
- φ = 0.20 —
- nwheels = 2 —
Solution
Step 1 — compute the bridge self-weight share carried by one end truck. The girder is symmetrical so each end truck carries half:
Step 2 — at the nominal worst case, the trolley sits at its end stop 0.6 m from the near rail. The lever-arm fraction of trolley + load carried by the near end truck is (L − a) / L:
Step 3 — add the bridge share, divide across 2 wheels per end truck to get nominal peak wheel load:
Step 4 — at the low end of operating reality, the trolley sits centred (a = 11 m). Now the trolley + load splits roughly 50/50 across both end trucks and impact drops to a static lift case (φ ≈ 0):
That is less than 40% of the worst-case wheel load — which is why runway beam designers always size on the end-stop position, never the centred position. At the high end, if the operator slams the up-button while the trolley is parked at the stop and the hoist is in a Class F harsh-duty pattern, φ rises to 0.30 and Pwheel,high climbs to about 90 kN per wheel — a 7% jump that can take a marginally-sized ASCE 60 rail past its allowable bearing stress.
Result
Nominal worst-case wheel load is 83. 5 kN, or about 8.5 tonnes per wheel — that sets the runway rail to ASCE 85 lb/yd minimum and the wheel diameter to 315 mm in standard Demag DRS sizing. In the centred-trolley low case the wheels see only 30.9 kN, and in the harsh-duty high case they reach 90 kN, so the 60 kN spread tells you the runway beam and column brackets must be designed for the end-stop case even though the crane spends 80% of its life nearer the centre. If you measure wheel load in service (with a strain-gauged wheel block) and read 95+ kN where you predicted 83 kN, the usual culprits are: end truck skew of more than 3 mm out of square loading one rail heavier than the other, a worn wheel flange riding up on the rail head and adding side thrust that the formula does not capture, or runway elevation drift letting the bridge sit lower on one side. Check rail parallelism with a tape across diagonals before you blame the hoist.
Travelling Crane vs Alternatives
A travelling crane is not always the right answer — sometimes a jib crane, a gantry crane, or a forklift moves the load cheaper, faster, or with less infrastructure. Compare on the dimensions that actually drive the buy decision: capacity, coverage, headroom cost, and cycle time.
| Property | Travelling Crane (overhead bridge) | Jib Crane | Gantry Crane |
|---|---|---|---|
| Load capacity range | 1 to 500+ tonnes | 100 kg to 10 tonnes | 1 to 100 tonnes |
| Coverage area | Full rectangular bay | Arc swept by the boom only | Rectangular strip under the gantry track |
| Lift speed (typical) | 3 to 8 m/min main hoist | 3 to 6 m/min electric chain hoist | 3 to 6 m/min |
| Long travel speed | 20 to 40 m/min | Not applicable (fixed pivot) | 10 to 30 m/min |
| Building infrastructure cost | High — runway beams, columns, often building re-engineering | Low — single column or wall mount | Medium — needs floor track or rails |
| Headroom required above load | 1.0 to 1.5 m for the hoist + girder | 0.6 m below the boom | 1.5 to 2.5 m for the legs and end carriage |
| Service life (CMAA Class C) | 20+ years, 500,000 cycles | 15 years, 250,000 cycles | 20 years if indoor, less outdoor |
| Best application fit | High-cycle heavy lifting across a full bay | Spotting lifts at one workstation | Outdoor yards or buildings without runway-capable structure |
Frequently Asked Questions About Travelling Crane
Matched motors do not fix a misaligned runway. If the two rails are out of parallel by more than span/1000 — about 20 mm on a 20 m span — the wheels on the wide side cover more distance per revolution than the narrow side, and the bridge skews. The VFDs read motor current, see one side working harder, and try to slow it down, which makes the skew worse on the next start.
Pull a tape across the diagonals of your runway from rail-clip to rail-clip. If the two diagonals differ by more than 6 mm, fix the rail before you blame the drive. Worn wheel flanges on one side only is the second telltale — that flange has been doing the job of keeping the bridge square.
Static wheel load is only half the story. CMAA 70 requires you to apply a vertical impact factor for hoisting and a horizontal inertia factor for bridge and trolley acceleration — the horizontal factor pushes the wheel against the rail head sideways, and that's what causes mushrooming on the gauge face.
Check whether your hoist is starting full-speed instead of two-step. A direct-on-line hoist contactor on a 10 tonne load drives the impact factor close to 0.4 instead of the 0.2 you probably designed for. Either retrofit a soft-starter or upgrade the rail to ASCE 85 minimum.
Three triggers push you to double-girder. First, capacity above roughly 15 tonnes — single-girder underhung trolleys run out of flange bearing capacity. Second, hook height — a top-running double-girder gains you about 1 m of extra lift because the trolley sits between the girders, not below them. Third, span over 22 m — the deflection penalty on a single-girder past that point forces a heavier section than two parallel girders.
Below 15 tonnes and 20 m span the single-girder is cheaper, lighter, and easier to install. Hyundai, Demag, and Konecranes all publish capacity-vs-span curves that show the crossover clearly.
That drift is the time gap between the motor de-energising and the brake fully clamping. On a DC disc brake — common on Stahl, R&M, and Demag hoists — coil voltage drops to zero at button release and the spring forces the disc shut, but if the brake disc is glazed or oil-contaminated, the disc slips for half a second before grabbing. 50 mm of drift at 6 m/min lift speed is exactly that half-second window.
Pull the brake cover and look at the friction face. A polished mirror finish is glaze; a dark stain is gear oil migrating past a failed gearbox seal. Replace the disc and fix the seal — do not just turn up the spring tension, that hides the symptom and burns out the coil.
Yes, tandem operation is standard in steel mills and aerospace bays. The minimum spacing is set by the bridge end-truck length plus a buffer — typically 1.5 m of clearance between the closest faces of the two bridges, enforced by mechanical bumpers or a proximity-sensor anti-collision system.
The gotcha is the runway beam loading. Two cranes both parked near each other double the column reaction, and most existing runways were never designed for that. Before you add a second crane, get the runway re-analysed — Konecranes and Demag both offer this as a service. Ignore it and you crack the column-to-corbel weld.
That lurch is almost always backlash in the trolley gearbox combined with the trolley sitting against the festoon cable drag. At rest, the festoon pushes the trolley a few millimetres in one direction, taking up gearbox backlash on that side. When you command motion the opposite way, the motor has to drive through 2x the backlash before the wheels actually start turning — and by then the VFD ramp has already wound up to 30% speed, so the trolley jumps when the gear teeth finally engage.
Fix it by enabling the VFD's anti-backlash creep function (a 0.5-second low-frequency pulse before the main ramp), or shorten the festoon to reduce its cable drag. On older systems without that VFD feature, a stiffer ramp from 0 to 5 Hz over 2 seconds before the main acceleration also masks the issue.
Runway length is the deciding factor. Below about 60 m, festoon cable on a C-track is cheaper, simpler, and easier to maintain — you can replace a single trolley without shutting the bay. Above 60 m the festoon mass becomes a problem: the cable bunches at one end take 30+ trolleys, the drag pulls the bridge motor current up by 10-15%, and dust accumulation in the C-track derails trolleys.
Outdoor runways or dusty environments (foundries, cement plants) push you to conductor bar regardless of length — insulated copper bar with sliding carbon shoes shrugs off contamination that would seize a festoon trolley in months.
References & Further Reading
- Wikipedia contributors. Overhead crane. Wikipedia
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